Obama also called Donald Trump's suggestion that the Nov. election might be rigged "ridiculous"

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President Barack Obama will speak after meeting Thursday with military and national security advisers at the Pentagon.

President Barack Obama is assessing what's working and what's not in the fight against the Islamic State group as the U.S. military ramps up its engagement in Libya.

Obama said Thursday there have been gains in weakening ISIS in Iraq and Syria, but he conceded that the extremist group is shifting its tactics to carrying out attacks elsewhere around the world.

"It still creates the kinds of fear and concern that elevates their profile," he said at a news conference after meeting with military and national security advisers at the Pentagon.

The president also pushed back at Republican nominee Donald Trump's suggestions that the November election might be rigged, calling the assertion "ridiculous." He said his advice to Trump, a candidate he has declared "unfit" for the presidency, was to "go out there and try to win the election."

Trump and Democratic nominee Hillary Clinton will soon be receiving classified briefings, giving them access to sensitive information about national security threats and the U.S. military posture. Asked whether he was worried about Trump having access to such material, Obama said simply that those who want to be president need to start acting like it.

"That means being able to receive these briefings and not spread them around," he said.

The session comes as the U.S. is bombing targets in and around the Libyan city of Sirte, a notable expansion of the U.S.-led coalition's military mission against ISIS. At the urging of the Pentagon, Obama authorized the strikes that started this week and include precision strikes against ISIS tanks, rocket launchers and fighting positions.

Obama typically convenes meetings of the National Security Council at the White House, but over the past year he has occasionally held them at other agencies like the State Department and the CIA. The goal of the road show at the Pentagon is to illustrate the multifaceted U.S. approach to defeating IS.

Mired in chaos following the ouster of strongman Moammar Gadhafi in 2011, Libya became a target for ISIS extremists hoping to build a safe haven outside its initial territory in Iraq and Syria. Though the number of ISIS fighters in Libya has dwindled, the U.S. is hoping to help Libya's fledgling, U.N.-backed unity government finish the job.

Obama used the meeting at the Pentagon to tout recent gains by the U.S. and its partners against IS in Syria and Iraq. With significant U.S. help, Iraq's government is preparing a major offensive to reclaim the key northern city of Mosul, controlled by ISIS since June 2014.

But he warned against posing the fight against ISIS as "a clash of civilizations," since that "plays exactly into the hands of ISIL and the perverse interpretations of Islam that they’re putting forward."